Preparation of methylpentalane



United States Patent 3,188,358 PREPARATION OF METHYLPENTALANE Abraham Schneider, Over-brook Hills, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No Drawing. Filed Aug. 7, 1962, Ser. No. 215,286 12 Claims. (Cl. 260-666) This invention relates to the preparation of methylpentalane from hydrindane by means of an aluminum halide catalyst. The invention also embraces the preparation of dimethylperhydropyrene as an additional of the reaction.

Hydrindane is a dicyclic C naphthene hydrocarbon having the following structure:

product It can exist in both cis and trans forms which have boiling points of about 166 C. and 159 C., respectively. Hydrindane can be derived by hydrogenating either indane or indene, which aromatics can be made from coal tar and petroleum fractions in known manner.

The .present invention provides a process for converting hydrindane to methylpentalane which has the following structure:

talane produced in the reaction has a boilingpoint approximating 150 C. and it exhibits only a single sharp peak when the reaction product is analyzed by vapor phase chromatography.

In accordance with the invention methylpentalane is prepared by contacting hydrindane, which can be either the cis or trans form or a mixture of these isomers, with an aluminum halide catalyst at a temperature in the range of 10 C. to 50 C., more preferably C to C.

After sufficient contacting of the hydrocarbon with such catalyst, methylpentalane can be separated from the reaction mixture in good yield by distillation. When the reaction is carried out at low temperature vw'thin the range specified, small amounts of C -C parafiins are formed as by-products, while at relatively high temperamres additional by-products are formed as hereinafter shown;

. As a further aspect of the invention dimethylperhydropyrene can be produced as an additional product of the reaction. This is a C polycyclic naphthene having four condensed rings and two methyl substituents. As

obtained in the present process, this compound appears to -be a single isomer having the following structural formula:

V V, on the charm, such as drmethylhexanes, trimethylpentanes 3,188,358 Patented June 8, 1965 It is a normally solid crystalline material having a melting point of about 187-190 C. When it is desired to obtain this compound in good yield in addition to methylpentalane, contact of the hydrindane with the aluminum halide catalyst should be carried out at'a temperature in the range of 2050 C. The dimethylperhydropyrene can readily be separated from other hydrocarbon products by crystallization from the reaction mixture at temperatures, for example, of 0- 32" C. Its separation can also be done easily by distillation, since it is muchhigher boiling than any other product obtained from the reaction.

The formation of methylpentalane from hydrindane in the present process is due to an isomerization reaction which, as I have discovered, favors the pentalane type of structure over the hydrindane type. The formation of dimethylperhydropyrene, however, is due to a different type of reaction that involves dimerization. The mechanism for this appears to be as follows. As the methylpentalane content builds up in the reaction mixture, there is a tendency for one of its rings to rupture especially at the higher reaction temperatures. This causes the formation of a C unsaturated monocyclic material which then becomes saturated by abstraction of hydrogen from either the unreacted hydrindane or the uncracked methylpentalane product or both. Whether the hydrogen is abstracted preferably from the hydrindane or the'methylpentalane product is notknown; but in any event one or the other or both of the C dicyclic components lose hydrogen and, under the influence of the catalyst, the resulting unsaturated material is transitory and immediately dimerizes to produoea C product, namely, the dimethylperhydropyrene.

I When the reaction is conducted at low temperatures such as -5 C. to 10 C., little rupturingof a ring of the methylpentalane product occurs and hence the amount of dimethylperhydropyrene formed is small. However, at temperatures in the range of 20-50 C., this ring rupturing reaction becomessubstantial and aconsiderable 1 zenes, mainly mesitylene and pseudocumene with a small.

proportion of hemimellitene. Some of the trimethylcyclohexane isomers are gem compounds whichwill not undergo such dehydrogenation In an embodiment of the process preferred for use when it is desired to' produce dimethylperhydropyrene in good yield, an additional hydrocarbon feed component is incorporated in the reaction mixture for the purpose of providing a material, other than the methylpentalane prodnet, that will readily undergo crackingand trigger the di; .merization reaction referred to above. The additional feed component employed for this purpose is paraflinic hydrocarbon having at least seven carbon'atoms er molecule andmore preferably at least eight. One' or more C-, or higher parafiinic hydrocarbons can be included in the reaction. mixture for this purpose. Mostpreferably, isoparaiiins are used which have a plurality of branches or any multiply branched isoparaflins of higher molecular weight. These paraffins in the presence of the aluminum halide catalyst will readily crack to form unsaturated intermediates which immediately abstract hydrogen from the unreacted hydrindane or the methylpentalane product or 'both and thus trigger the dimerization reaction. The parafiinic material used thus becomes converted mainly to lower isoparafiins of the C -C range, with isobutane being the isoparafiin formed in largest amount. The reacton preferably is conducted at a temperature of C. to 10 C. to avoid cracking of the methylpentalane product of the reaction. The paraflin component of the charge will readily crack under these conditions while the methylpentalane formed will not undergo any substantial amount of ring rupturing.

In the foregoing embodiment of the invention in which a parafiin component is included in the reaction mixture, it is preferable to use a molar ratio of hydrindane to the parafiin in the range of 3:1 to 10:1. At ratios in this range and using a reaction temperature in the range of 5 C. to 10 C., the reaction will proceed cleanly without substantial deactivation of the catalyst and good yields of both methylpentalane and the dimer product (dimethylperhydropyrene) can be obtained. Any unreacted hydrindane can be recovered from the reaction product and recycled for reuse.

An aluminum halide catalyst obtained by combining AlCl with HCl or AlBr with HBr is used to effect the reactions contemplated within the scope of the invention. With either aluminum halide the catalyst preferably is a liquid complex obtained by reacting the aluminum halide and hydrogen halide in the presence of one or more parafiin. hydrocarbons having at least seven and more preferably at leasteight carbon atoms. When AlCl is used it is preferable to use paraflin hydrocarbons which have more than eight carbon atoms. This complex type of catalyst is insoluble in the reaction mixture, and the activity of the catalyst depends upon having at least a small amount of uncomplexed A1Cl or AlBr present therein. The catalyst complex is a colored mobile liquid and typically in the case of AlBr is bright orange-yellow. In preparing the complexany paraflin hydrocarbon or mixture of such paratiins having seven or more carbon atoms can be used, but it is desirable to use a branched paraffin, e.g., one having at least two branches, in order to reduce the time for preparing the complex and it is particularly preferred that such isoparaifins have at least eight carbon atoms per molecule.- A slow degradation of the catalyst may occur over a course of time, particularly when AlBr is used to make the catalyst, but the addition of a small amount of fresh aluminum halide from time to time will reactivate the catalyst. Also a portion or all of the catalyst complex can be replaced from time to time by fresh catalyst complex to maintain catalytic activity.

Preparation of the catalyst complex comprises dissolving or suspending the aluminum halide in the parafiin hydrocarbon and passing the hydrogen halide into the mixture. This can be done at room temperature, although the use of an elevated temperature such as 50 100 C. generally is desirable to increase the rate of reaction; For best results at least five moles of the paraffin per mole of AlCl or AlBr should be employed. Under these conditions some of the paraffin evidently breaks into fragments, yielding a 0.; fragment whichrbeco'mes the hydrocarbon portion of the complex. In' the case of AlBr as the reaction proceeds the mixture becomes milky and the orange-yellow liquid complex then precipitates fromthe hydrocarbon phase. Addition of HBr is continued until the milky appearance has disappeared.

For obtaining the most active catalyst complex the addition of HBr should be stopped at this point. When AlCl is used to make the catalyst,such milky appearance .does

hexanes at about 50 C. for about 30 minutes.

not appear as the HCl is added. Instead the particles of AlCl in suspension in the hydrocarbon merely become converted to the liquid complex. The addition of HCl is stopped before all of the AlCl reacts so that the complex formed will contain some AlCl particles suspended therein. The resulting complexes made with either AlCl or AlBr are relatively stable materials having high catalytic activity.

When the aluminum halide is AlBr the catalyst can also be used with the AlBr dissolved in the hydrocarbon reactant so that the reaction mixture is homogeneous. When using this type of catalyst system, the A1Br is dissolved in the hy-drindane, or the mixture of hydrindane and paraffin hydrocarbon as the case may be, to the extent of 5200% by weight on the total hydrocarbon and HBr is pressured into the mixture in amount of at least 0.25% by weight of the hydrocarbon. The resulting reaction mixture remains homogeneous as the reaction occurs. With AlCl a homogeneous system cannot be used since AlCl is essentially insoluble in hydrocarbons.

The present process is carried out by contacting the aluminum halide catalyst with the hydrocarbon reactant at a suitable temperature within the general range of 10 C. to 50 C. The temperature within this range should be selected in accordance with considerations as indicated above, depending upon whether or not it is desired to produce the C dimer as product and whether or. not a crackable paraffin component is included in the feed. When the reaction is carried out employing the catalyst in the preferred complex form as described above, the reaction mixture sould be vigorously agitated to provide intimate contact between the hydrocarbon and catalyst phases. The time allowed for reaction will vary depending largely upon the reaction temperature selected but generally should be in the range of 10 minutes to 10 hours. After the desired degree of conversion has been reached, the catalyst is separated from the hydrocarbon material and the latter can be distilled to obtain the desired product or products. When an aluminum halide complex is used as catalyst, the reaction mixture can be settled to separate the complex phase from the hydrocarbons and the catalyst complex can be recycled and reused. The hydrocarbon phase can, if desired, be washed with water to remove any catalyst residues prior to being fractionated into the desired products. When AlBr -HBr is used as a soluble catalyst, the HBr and hydrocarbons can be separately recovered by distillation from the AlBr and the hydrocarbons can then be fractionated to yield appropriate product fractions.

The following example more specifically illustrates the invention.

EXAMPLE A catalyst complex was prepared by bubbling HBr into a mixture of 5 g. ofAlBr and 8 ml. of mixed dimethyl- Thereafter the unreacted hydrocarbons were decanted from the catalyst complex layer and about 3 ml. of the layer were obtained. This was a mobile oily liquid having an orangeyellow color. The reaction was carried out in a rocker bomb by contacting the catalyst with 5 mLof hydrindane obtained by hydrogenating indane using a Raney nickel catalyst. The hydrindane was composed of 84.1% and 15.9% by weight of its cis and trans isomers, respectively. The temperature initially was maintained at 0 C. and small samples of the hydrocarbon product were taken for analysis at total reaction times of 5, 65 and 290 minutes. Then the temperature was raised at 2829 C., the reaction was continued and samples of the hydrocarbon product were taken at overall reaction times of 322 minutes and 5 62 minutes. Analytical results obtained by vapor phase chromatography are shown in the accompanying table.

Table Cut No 1 2 3 4 5 Reaction temperature 0 0 0. 0 C. 28 C. 29 C.

Total reaction time, min 65 290 322 502 Composition of product, weight percent:

C4 parafiins 2. 8 3. 0 2.8 2. 7 1. 9 C5 paraflins 2.3 2.7 2.6 2. 7 2.3 Ci parafiins 1. 5 1. 4 1. 4 1. 3 1. 1 C1paratfins 0.7 1.0 1.0 0.8 0.7 01 monocyclic nanhtbenes Trace Trace 0. 1 0. 4 C monocyclic naphthenes Trace 0. 2 0. 04 0. 7 C monocyclic naphthenes Trace Trace 0. 2 0. 6 13. 0 C10 monocyciio nanhthenp: Trace 2. 1 Methylpentalane 0. 6 25. 4 63. 5 57. 9 39. 7 Trans-hydrindane 55. 7 41. 5 16. 5 15. 7 9. 1 Cis-hydn'ndane 36. 1 23. 2 4. 0 2. 5 2. 5 Debalin 0. 1 Methylrler alin Trace 0. 1 Dimethyldecalins- Trace 0. 4 Trimethyldecalins 0. 2 0. 5 0. 6 g 0. 5 0. 8 Dimethylperphydropyrene 1. 2 7. 4 15. 1 25. 1

The data presented in the table show that reaction at The methylpentalane produced by the present process 0 C. will produce methylpentalane as the major product can be converted into dlcyclic C diolefins by dehydroand that only a small amount of dimethylperhydropyrene is formed even when a long reaction time such as five hours is used. However by raising the temperature to a higher level such as 2530 C., the formation of the C dimer becomes substantial and the content of methylpentalane previously formed will decrease. Concurrent with the formation of the dimer at the higher temperature level, the production of C monocyclic naphthenes occurs to appreciable extent as shown by the 13% concentration of these components in the final reaction products.

These C monocyclic naphthenes are essentially all trimethylcyclohexanes and include a substantial proportion of gem compounds, typically, of the order of Upon dehydrogenating the mixture of trimethylcyclohexane isomers using a platinum-on-alumina catalyst at 370 C., the product typically has the following composition by weight:

The undehydrogenated gem compounds can readily be distilled from the trimethylbenzenes formed and obtained as a separate product. If desired these gem compounds can be recycled to the primary reaction zone where they will equilibrate, forming additional non-gem isomers that can be dehydrogenated to increase the yield of the trimethylbenzenes.

In the specific example described above it was found that as the concentration of the dimer builds up in the reaction mixture it tends to crystallize therefrom. Thus for Cut No. 3 a small amount of crystals could be observed in the reaction mixture at 0 C. With Cut No. 4 no dimer crystals were observed at room temperature but there Wa s considerable precipitate upon cooling to 0 C. With Cut No. 5 there was a heavy precipitate of dimer even at room temperature. It is therefore apparent that when the reaction is carried out to produce a high yield of the dimethylperhydropyrene most of it can be recovered from the other hydrocarbon products simply by filtration. The dimethylperhydropyrene which remains in solution in the liquid hydrocarbons at the filtration temperature employed can be obtained from the filtrate by distilling ed the other hydrocarbons. In cases where methylpentalane is not desired as a product of the process, it and any unreacted hydrindane can be separated from the other reaction products and recycled to the reaction zone to increase the yield of dimethylperhydropyrene.

genation over a suitable catalyst such as chromia-on-aluminum or copper chromite. The dicyclic diolefin product can be used as charge'material for special polymerization and dimerization reactions.

I claim:

*1. Method of preparing methylpentalane and dimethyl perhydropyrene which comprises contacting a mixture of hydrindane and parafiin hydrocarbon having at least seven carbon atoms with an aluminum halide catalyst at a temperature in the range of 5 C. to 10 C., and separating methylpentalane and dimethylperhydropyrene from the reaction mixture.

2. Method according to claim 1 wherein the molar ratio of hydrindane to said paraflin hydrocarbon is in the range of 3:1 to 10:1.

3. Method according to claim 1 wherein said paraflin is isoparaflinic hydrocarbon having at least eight carbon atoms.

4. Method according to claim 3 wherein said catalyst is a pro-formed liquid complex obtained by reacting AlCl HCland paraffin hydrocarbon having at least seven carbon atoms.

5. Method according to claim 3 wherein said catalyst is a pre-formed liquid complex obtained by reacting AlBr HBr and parafiin hydrocarbon having at least seven carbon atoms. a

6. Method of making dimethylperhydropyrene which comprises contacting hydrindane and recycle material hereinafter specified with an aluminum halide catalyst at a temperature in the range of 20-50 C., whereby dimethylperhydropyrene, methylpentalane and other hydrocarbon products are formed, recovering dimethylperhydropyrene and methylpentalane separately from the reaction mixture, and utilizing the recovered methylpentalane as said recycle material.

7. Method according to claim 6 wherein said catalyst is a pre-formed liquid complex obtained by reacting AlCl3, HCl and paraffin hydrocarbon having at least seven carbon atoms.

8. Method according to claim 6 wherein said catalyst is a pre-formed' liquid complex obtained by reacting AlBr HBr and paraffin hydrocarbon having at least seven carbon atoms.

9. Method of making dimethylperhydropyrene which comprises contacting hydrindane with an aluminum halide catalyst at a temperature in the range of -10 C. to 50 C., whereby isomerization occurs with the formation of methylpentalane, continuing the contacting with said catalyst at suchjtemperature until at least a substantial amount of a separate phase comprising crystalline dimethylperhydr-opyrene has been formed, and separating crystalline dimethylperhydropyrene from the reaction mixture.

10. Method according to claim 9 wherein the temperature is in the range of 20-50 C.

11. Method according to claim 9 wherein the contacting with the catalyst is done in the presence of parafiin hydrocarbon having at least seven carbon atoms and at a temperature in the range of 5 C. to 10 C.

12. Method according to claim 11 wherein the molar ratio of hydrindane to paraifin hydrocarbon used is in the range of 3:1 to 10:1.

8 References Cited by the Examiner UNITED STATES PATENTS 2,396,331 3/46 Marschner 260-666 OTHER REFERENCES Thomas: Anhydrous Aluminum Chloride in Organic Chemistry, p. 791 relied on, Reinhold Publishing Corporation, N.Y., 1941.

Zelinski et 211.: Ben, vol. 62, pp, 1658-63, 1929.

AL'PHONSO D. SULLIVAN, Primary Examiner. 

9. METHOD OF MAKING DIMETHYLPERHYDROPYRENE WHICH COMPRISES CONTACTING HYDRINDANE WITH AN ALUMINUM HALIDE CATALYST AT A TEMPERATURE IN THE RANGE OF -10*C TO 50* C., WHEREBY ISOMERIZATION OCCURS WITH THE FORMATION OF METHYLPENTALANE, CONTINUING THE CONTACTING WITH SAID CATALYST AT SUCH TEMPERATURE UNTIL AT LEAST A SUBSTANTIAL AMOUNT OF SEPARATE PHASE COMPRISING CRYSTALLINE DIMETHYLPERHYDROPYRENE HAS BEEN FORMED, AND SEPARATING CRYSTALLINE DIMETHYLPERHYDROPYRENE FROM THE REACTION MIXTURE. 